A good friend of mine went through this, so that's why I started introducing the sippy a long time ago to make sure he was good at it before I started the transition to milk. I
My suggestion after watching my friend go through this is to stand your ground and do NOT give him a bottle. It will be hell for a few days but eventually he'll learn that he doesn't get the bottle anymore. If he's thirsty enough, he'll take the sippy cup.